1. Field of the Invention
The present invention relates to a magnetic recording and reproduction apparatus, and more particularly to a magnetic recording and reproduction apparatus having means for evaluating the degree of data accuracy and means for detecting a fault to assure the quality of the apparatus.
2. Description of the Related Art
A magnetic recording and reproduction apparatus having a Viterbi detector is described in IEEE Transactions on Magnetics, Vol. 27, pp. 4538-4543.
This magnetic recording and reproduction apparatus is made up of a write precompensation circuit for correcting a bit shift which is generated at the time of reproduction, a low-pass filter for removing high-frequency noise components of an analog reproduction waveform signal read from a magnetic recording medium, an A/D converter for converting the analog reproduction waveform signal into a digital waveform signal, a waveform equalizer for shaping the digital waveform signal, and a Viterbi detector for identifying digital data from the shaped ditigal waveform signal. In this apparatus, a recording-reproduction signal processing circuit is contained in a one-chip LSI (Large Scale Integrated Circuit) to meet requirements for reduction in size and increase in data transfer rate.
A criterion for deciding the quality of a magnetic recording and reproduction apparatus is the degree of data accuracy. The degree of data accuracy is dependent on the recording-reproduction channel parameters such as the amount of write precompensation of the write precompensation circuit, the cut-off frequency of the low-pass filter, and the equalization coefficient value of the waveform equalizer, as well as the electromagnetic conversion characteristics of a magnetic head and a magnetic medium. For producing a magnetic recording and reproduction apparatus of high quality, these parameters are required to be set to optimum values at the time of using the apparatus. In order to determine the optimum value of these parameters, on the other hand, the degree of data accuracy is required to be evaluated quantitatively at the time of parameter variations.
Generally, an error rate is used as a numerical value for quantifying the degree of data accuracy. When a magnetic recording and reproduction apparatus is being used under normal operating conditions, however, the error rate is so small that the measurement of the error rate requires a great amount of time, thereby making it difficult to decide the quality of the apparatus accurately.
JP-A-3-144969 discloses a technique in which the degree of data accuracy is evaluated by comparing the series of a digital waveform signal with the series of a reference signal, measuring the histogram of the resulted error value, and thus predicting the data error rate of the magnetic recording and reproduction apparatus.
On the other hand, as a conventional method of evaluating the degree of data accuracy, a level margin test is known. In the level margin test, a gate slice level to be compared with the amplitude of an output signal of the waveform equalizer is moved vertically, and by detecting missing bits or extra bits, the margin width of the gate slice level and the data error rate are measured.
The method of predicting an error rate by histogram measurement, however, emphasizes only the distribution of a digital waveform signal and fails to incorporate the data identification characteristics of the Viterbi detector for estimating a series of maximum likelihood values. The level margin test, which detects a level for each bit, also does not incorporate the data identification characteristics of a Viterbi detector for estimating a series of maximum likelihood values. For these reasons, the conventional methods of evaluating the degree of data accuracy cannot correctly evaluate the performance of the recording-reproduction channel including the Viterbi detector.
In the case where a recording-reproduction signal processing circuit is built in an LSI chip, it is not easy to detect an optimum value of a parameter unless the same chip includes means for evaluating the dependency of the magnetic recording and reproduction apparatus on the recording-reproduction channel parameters. Further, it is also not easy to determine the quality of the magnetic recording and reproduction apparatus.
An object of the invention is to provide a magnetic recording and reproduction apparatus having a Viterbi detector capable of evaluating the degree of data accuracy of the apparatus.
Another object of the invention is to provide a magnetic recording and reproduction apparatus capable of evaluating the degree of data accuracy of the apparatus by changing the circuit characteristics of the apparatus.
Still another object of the invention is to provide a magnetic recording and reproduction apparatus capable of measuring the data error rate in accordance with a predetermined sequence.
In order to achieve these objects, according to one aspect of the invention, there is provided a magnetic recording and reproduction apparatus made up of a data generator for generating write data, a write precompensation circuit for correcting the phase of the write data signal generated from the data generator, and a magnetic head for electromagnetically converting the write data signal corrected by the write precompensation circuit, a magnetic disc moved relatively with the magnetic head for recording and reproducing a signal through the magnetic head, a read-write amplifier amplifies the signal recorded in the magnetic head and read from the magnetic head, and an AGC circuit keeps constant the amplitude of the output signal of the read-write amplifier. The apparatus further includes a low-pass filter for removing the high-frequency noise components of the output signal of the AGC circuit, an A/D converter for sampling the output signal of the low-pass filter and converting it into a multi-valued digital value, a waveform equalizer for shaping the digital signal converted by the A/D converter, and a VFO circuit for producing a sample clock of the A/D converter, A Viterib detector identifies the output signal of the waveform equalizer by two threshold values and produces read data based on the sample clock. The apparatus further employs and means for changing the reference amplitude value providing the threshold level of the Viterbi detector, means for comparing the write data and the read data, and means for detecting an error, wherein data is recorded and reproduced with the reference amplitude value changed. The degree of data accuracy of the magnetic recording and reproduction apparatus is evaluated according to the data error rate of the apparatus which was measured by changing the reference amplitude value of the Viterbi detector.
According to another aspect of the invention, there is provided a magnetic recording and reproduction apparatus wherein a signal processing LSI has a function such that at least an input pin of the LSI is designated, through which the reference amplitude value of the Viterbi detector is changed.
According to still another aspect of the invention, there is provided a magnetic recording and reproduction apparatus which has the function of changing the cut-off frequency of a low-pass filter, the equalization coefficient value of a waveform equalizer and the reference amplitude value of a Viterbi detector. The degree of data accuracy of the magnetic recording and reproduction apparatus is evaluated by measuring the data error rate when the reference amplitude value of the Viterbi detector is displaced from a reference value while changing the cut-off frequency of the low-pass filter and the equalization coefficient value of the waveform equalizer.
According to a further aspect of the invention, there is provided a magnetic recording and reproduction apparatus which has the function of changing the amount of write precompensation of a write precompensation circuit and the reference amplitude value of a Viterbi detector. While changing the write precompensation amount of the write precompensation circuit, the data error rate is measured with the reference amplitude value of the Viterbi detector displaced from a reference value. Thus the degree of data accuracy of the magnetic recording and reproduction apparatus is evaluated.
According to a still further aspect of the invention, there is provided a magnetic recording and reproduction apparatus wherein the write precompensation amount of a write precompensating circuit, the cut-off frequency of a low-pass filter, the equalization coefficient value of a waveform equalizer, and the reference amplitude value of a Viterbi detector are set automatically in accordance with a sequence predetermined by a coefficient setting sequencer.
According to a yet further aspect of the invention, there is provided a magnetic recording and reproduction apparatus wherein the degree of data accuracy of the apparatus is evaluated by measuring the magnitude of a signal obtained by averaging the absolute value or the square value of the waveform equalization error.
According to the present invention, the data identification performance can be deteriorated while maintaining the identification characteristics of a Viterbi detector of the magnetic recording and reproduction apparatus by displacing the reference amplitude value of the Viterbi detector from a reference value. As a result, a data error occurs with an increasing frequency, thereby making it possible to measure the data error rate within a short length of time. The data error rate inherent to the apparatus, i.e., the degree of data accuracy of the apparatus, can thus be predicted from the particular data error rate.
Further, the signal processing LSI has the function of changing the reference amplitude value of a Viterbi detector through an input pin of the LSI. As a result, the degree of data accuracy of the apparatus can be easily evaluated with an LSI built in the apparatus.
Furthermore, the data error rate is measured with the cut-off frequency of a low-pass filter and the equalization coefficient value of a waveform equalizer changed while displacing the reference amplitude value of a Viterbi detector from a reference value. The effect of a change in the reproduction channel parameter on the data accuracy is evaluated, and an optimum value of the parameter can thus be determined.
In addition, according to the invention, the effect of a change in the amount of write precompensation on the degree of data accuracy can be evaluated by changing the write precompensation amount of the write precompensation circuit of the magnetic recording and reproduction apparatus and measuring the data error rate with the reference amplitude value of the Viterbi detector displaced from a reference value, thereby determining an optimum value of the write precompensation amount.
Also, the magnetic recording and reproduction apparatus according to the invention has the function of automatically setting the cut-off frequency of the low-pass filter, the equalization coefficient value of the waveform equalizer and the reference amplitude value of the Viterbi detector in accordance with a sequence predetermined by a coefficient setting data sequencer. As a result, the degree of data accuracy can be easily evaluated while setting the coefficient automatically in accordance with a predetermined sequence without using any external devices such as a controller.
What is more, the data identification performance of the recording-reproduction channel can be approximately grasped by monitoring the signal representing the average of the absolute value or the square value of the waveform equalization error. As a consequence, the result of a quality assurance test of a product and the chronological change of the recording-reproduction channel including the head disc when being used by the user after the product shipment can be determined.